Gamma Cameras are used for the detection of gamma rays, typically in the energy range of 40 keV to 511 keV. These cameras can be designed with collimators, scintillators, detectors and electronics, with the detectors being of tube or silicon design, or they may use a more direct detection method that combines the scintillator and detector into a single material, in the manner that is used within CZT cameras. These camera systems are used in medical imaging, pre-clinical imaging, veterinary imaging, and for a variety of other uses including radiation imaging for radioactive material and hazardous material inspection.
Recent advances in silicon photomultiplier detector technology have allowed for a significant reduction in the size of the detector portion of the gamma camera as compared to tube photomultipliers. Examples of silicon photomultipliers are available commercially from companies such as SensL and Hamamatsu. These detectors can be made with pixel sizes from 1 mm to 6 mm, for example, and each pixel has many sub-pixels, of typical size 35 micrometers.
Previously, photomultiplier tubes were used as the detectors in gamma cameras, which caused the camera depth to be many inches. While the scintillator material may be only 5 mm in some cases and the collimator element may only be 20 to 30 mm in some cases, the large size of the tube photomultiplier, and the need for fairly high voltages to be used in tube-based designs, dominated the product design.
Silicon-based detectors of thicknesses measured in mm are now possible, with a depth of 2 to 5 mm or less being possible in some package designs. In addition, the tubes would typically be of a diameter that was an inch or more, whereas the silicon photomultipliers can be made with 1 mm diameters. A recent check of the Hamamatsu website indicated that part R7402 was a compact tube design, and it had a diameter of 16 mm, only 8 mm of which was the “working” or sensing part of the tube. This is in comparison to the SensL products that are currently available, such as the Array 4, which allows a set of 16 photomultipliers of size 3.3 mm×3.3 mm, in a 4 by 4 array, giving a total size of 14 mm×14 mm, including packaging sizes.
Gamma camera systems today can be designed to give two dimensional (planar) or three dimensional images. In order to provide three dimensional imaging, it is necessary to add information from another angle or direction. This approach is called SPECT imaging, and it can be performed either by moving a single gamma camera head between multiple positions or by having more than one gamma camera head located in the multiple positions.
U.S. Pat. No. 5,565,684 entitled Three-dimensional SPECT reconstruction of combined cone-beam and fan-beam data discusses the use of three gamma camera heads mounted onto a gantry for rotation about the patient.
Other SPECT systems are also known.
U.S. Pat. No. 6,242,743 entitled “Non-orbiting tomographic imaging system”, discusses the production of tomographic images without moving the detectors or collimators. This is done by “using a plurality of detector modules which are distributed about or around the object of interest and which fully or partially encircle it. The detector modules are positioned close to the object of interest thereby improving spatial resolution and image quality. The plurality of detectors view a portion of the patient or object of interest simultaneously from a plurality of positions. These attributes are achieved by configuring small modular radiation detector with high-resolution collimators in a combination of application-specific acquisition geometries and non-orbital detector module motion sequences composed of tilting, swiveling and translating motions, and combinations of such motions. Various kinds of module geometry and module or collimator motion sequences are possible, and several combinations of such geometry and motion are shown. The geometric configurations may be fixed or variable during the acquisition or between acquisition intervals. Clinical applications of various embodiments of the tomography invention include imaging of the human heart, breast, brain or limbs, or small animals. Methods of using the non-orbiting tomographic imaging system are also included.
U.S. Pat. No. 6,628,984, entitled, “Hand held camera with tomographic capability,” describes a tomographic imaging system comprising a moveable detector, a position sensor, and a computational device for integrating the position and angulation of the detector with the emissions that are observed. This allows for a derivation of a three dimensional image.
U.S. Pat. No. 5,939,724, to Eisen, et al., issued on Aug. 17, 1999, and entitled, “Light weight-camera head and -camera assemblies containing it,” describes a light weight gamma-camera head and assemblies and kits which embody it. The gamma-camera head has a detector assembly which includes an array of room temperature, solid state spectroscopy grade detectors each associated with a collimator and preamplifier, which detectors and associated collimators and preamplifiers are arranged in parallel rows extending in a first direction and suitably spaced from each other in a second direction normal to the first direction, each of the parallel detector rows holding a plurality of detectors. The head may optionally have an electric motor for moving the detector in the second direction and optionally also in the first direction, either stepwise or continuously.
U.S. Pat. No. 6,525,320, to Juni, issued on Feb. 25, 2003, and entitled, Single photon emission computed tomography system, describes a single photon emission computed tomography system, which produces multiple tomographic images of the type representing a three-dimensional distribution of a photon-emitting radioisotope. The system has a base including a patient support for supporting a patient such that a portion of the patient is located in a field of view. A longitudinal axis is defined through the field of view. A detector module is adjacent the field of view and includes a photon-responsive detector. The detector is an elongated strip with a central axis that is generally parallel to the longitudinal axis. The detector is operable to detect if a photon strikes the detector. The detector can also determine a position along the length of the strip where a photon is detected. A photon-blocking member is positioned between the field of view and the detector. The blocking member has an aperture slot for passage of photons aligned with the aperture slot. The slot is generally parallel to the longitudinal axis. A line of response is defined from the detector through the aperture. A displacement device moves either the detector module or the photon-blocking member relative to the other so that the aperture is displaced relative to the detector and the line of response is swept across at least a portion of the field of view.
U.S. Pat. No. 6,271,525, to Majewski, et al., issued on Aug. 7, 2001, and entitled, “Mini gamma camera, camera system and method of use,” describes a gamma camera, which comprises essentially and in order from the front outer or gamma ray impinging surface: 1) a collimator, 2) a scintillator layer, 3) a light guide, 4) an array of position sensitive, high resolution photomultiplier tubes, and 5) printed circuitry for receipt of the output of the photomultipliers. There is also described, a system wherein the output supplied by the high resolution, position sensitive photomultiplier tubes is communicated to: a) a digitizer and b) a computer where it is processed using advanced image processing techniques and a specific algorithm to calculate the center of gravity of any abnormality observed during imaging, and c) optional image display and telecommunications ports.
U.S. Pat. No. 6,212,423, to Krakovitz, issued on Apr. 3, 2001 and entitled, “Diagnostic hybrid probes,” describes a hybrid nuclear and ultrasonic probe, comprising a cylindrical outer casing surrounding a nuclear probe, which comprises two scintillator plates intersecting perpendicularly, each of the scintillator plates having a plurality of parallel collimators; and an ultrasonic probe situated between said casing at the intersection of said scintillator plates.
U.S. Pat. No. 7,705,316 entitled Dynamic SPECT camera discusses a SPECT camera that has a plurality of single-pixel detectors, which can be moved, and which includes a position-tracker that provides information on where the detectors are at each point in time, and which includes a time-binning method. In this way, radioactive emissions can be collected from different positions at different times, and then software can be used to create the 3D image at a later time.
U.S. Pat. No. 8,338,788 entitled Method and system of optimized volumetric imaging describes a system that performs a volumetric scan. The system uses a plurality of extendable detector arms with each detector arm having a detection unit, supported by an actuator and gantry. The types of methods that have been discussed in U.S. Pat. No. 8,338,788 and U.S. Pat. No. 7,705,316 attempt to control the position of the gamma camera heads using attachments on the back of the detector heads.
In the case where a single gamma camera head is moved, it will be moved between two or more positions in some known fashion, such as on a mechanical track, rail or arm. This approach will take a certain number of minutes at one location and then will move to the second location, where it will take another block of a certain number of minutes.
In the case where multiple gamma camera heads are available, the heads may be held in two or more positions for a certain number of minutes, as discussed in U.S. Pat. No. 7,705,316 or U.S. Pat. No. 8,338,788. Arms and gantries have typically been used to move the camera heads.
The first approach may be better for equipment cost, as long as the gamma camera head moving apparatus is less costly than the second head. The second approach is better if one wants to get an image in as short a time as possible, or if one is observing simultaneous radionuclide movements. Typical positioning methods allow two gamma camera heads to be between 40 and 90 degrees apart in order to have sufficient information to achieve good spatial resolution in all three directions. Another approach to SPECT imaging is to allow handheld operation of the gamma camera, and then to have positioning system and software automatically align the positioning information with the gamma camera counts information, thereby allowing a 3D image of the radiating object to be obtained. This method is used by SurgicEye in their designs, discussed in US patent application 20090259123.
The idea of using a flexible substrate to mount gamma detectors has been discussed in Published US Patent Application 20090321650. In this case, they are using a specific design of detectors that may be individually stimulated by a detector reader. Their intended application relates to radiation monitoring and security.
Interest in flexible scintillators has been shown in previous patents, including U.S. Pat. No. 6,563,120 entitled Flexible radiation detector scintillator, in which a plastic scintillator was cut in elongated slices, and these slices slid relative to one another to allow 2-d flexibility to be achieved.
Another approach to a flexible scintillator has been taken in U.S. Pat. No. 7,132,662 entitled Flexible liquid-filled radiation detector scintillator, which uses a tube filled with liquid scintillating material. These inventors also considered the thermal expansion concerns of the liquid.